In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n-type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p-type extrinsic material portions in a semiconductor wafer.
In general, it is desirable to provide uniform implantation of the surface of the workpiece. Accordingly, conventional systems often undergo a calibration operation to adjust a voltage waveform of a beam scanner to counteract the focal variation of the beam along the scan direction and/or to compensate for other beam irregularities. This is typically done in a point-to-point fashion by subdividing the profile region and the scanner voltage range into a series of discrete points that are equally spaced throughout the profile. For each discrete point, a measurement sensor is located at the point, and the scanned beam flux is measured at the point. After each measurement is completed, the measurement sensor steps to the next point, and then stops and performs another measurement. Such measurements are then repeated for each of the points, and the final scan waveform is adjusted to compensate for profile non-uniformities by assuming either a point beam or a beam profile constant across the scan.
Although the conventional point-to-point scanner calibration techniques may be adequate where the width of the ion beam is both narrow and relatively constant across the target area, these techniques are less suitable in the case of wider beams and/or in situations where the beam width varies along the scan direction. In particular, if the beam is wide and/or variable across the target area, the point-to-point technique fails to account for the workpiece dose produced by the beam some distance from the beam center. This situation is particularly problematic with low energy ion beams that experience space charge expansion (e.g., lateral divergence in the scan or X direction).
In addition, conventional point-to-point scanner calibration techniques require a considerable amount of time to obtain sufficient data. Typically, in conventional systems, the point-to-point measurements discussed above are taken over a number of beam passes in the X-direction. Because each beam pass may take several seconds, these conventional systems may often take several minutes to perform a single calibration. In scenarios where an ion implanter is recalibrated after a limited number of wafers (e.g., prototypes, test structures, etc.), this long calibration time significantly and adversely affects processing throughput.
Accordingly there is a need for improved ion beam scanner calibration techniques by which uniform implantation can be facilitated, in a reduced calibration time.